1. Field of the Invention
The invention relates to a carpet knife, and more particularly, to the carpet knife an active blade thereof is able to be stably fixed and simply exchanged.
2. Description of Related Art
Carpet knife is a kind of utility knife, which is a commonly used hand tool for cutting, e.g., wood, paper, leather, plastic panel, cord, cardboard, and particularly, carpet or rug. Shown in FIG. 5a is a conventional carpet knife 9. The carpet knife 9 usually has a housing made up of a right cover 91 and a left cover 92 detachably coupling together. FIG. 5b is a perspective view showing an inner side of the right cover 91. The right and the left cover 91 and 92 are fixed together to form the housing by a thumb screw 93. There is a blade chamber 94 defined in a front portion of the housing for containing an active blade 95. An active blade installation bar 96 is formed in the blade chamber 94. The active blade 95 is able to be installed in the blade chamber 94 with a central slot 951 thereof covering the active blade installation bar 96. When a user rotates to tighten the thumb screw 93, the right and the left cover 91 and 92 move closer with respect to each other and the active blade 95 will be able to be pressed and thus clamped by a touching surface 941 of the blade chamber 94. A spare blade installation bar 97 may be formed in the housing for placement of spare blades. The housing acts as both a handle and a container for active and spare blades.
Such kind of carpet knife has some drawbacks. First, the active blade 95 is not easily able to be stably fixed. If the user tighten the thumb screw 93 insufficiently, a tiny distance between touching surfaces 941 of the right cover 91 and the left cover 92 may cause cross movement of the active blade 95. However, if the user tighten the thumb screw 93 overly, the front portions of the right and the left cover 91 and 92 may warp and move apart, which also makes the active blade 95 unstable. Second, either in tightening or in releasing, a user usually has to rotate the thumb screw 93 a number of rounds. Together with finding and aligning a thumb screw hole, replacement of dull blade for such carpet knife takes longer time. Third, after repeatedly use, the thumb screw 93 is liable to loose, usually slightly, which may cause unstable of the active blade 95.